Golf club head

ABSTRACT

A golf club head includes a striking face, a crown and a sole. The crown and/or the sole includes an FRP member formed by a fiber reinforced plastic that contains a fiber and a matrix resin. The FRP member has an average flexural modulus of greater than or equal to 25 GPa. The fiber may contain a carbon fiber. The carbon fiber may have a tensile elastic modulus of greater than or equal to 300 GPa. The fiber may contain a metallic fiber. The FRP member may have a resin content of less than or equal to 40% by weight. The matrix resin may have a glass transition temperature of higher than or equal to 150° C.

The present application claims priority on Patent Application No.2018-173211 filed in JAPAN on Sep. 18, 2018. The entire contents of thisJapanese Patent Application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a golf club head.

Description of the Related Art

There has been known a golf club head including a crown that is formedby using a fiber reinforced plastic (FRP). The use of an FRP can improvethe degree of freedom in design of the head.

SUMMARY OF THE INVENTION

As compared with a head formed by only a metal, a head formed by usingan FRP is difficult to attain a good sound at impact. For many golfplayers, a sound at impact is more than a matter of mere preference. Thesound at impact can affect evaluation on the shot. The sound at impactcan have an effect on the golf player's state of mind. The sound atimpact can influence the swing.

The present disclosure provides a head that includes an FRP member andhas a high-pitched sound at impact.

According to one aspect, a golf club head includes a striking face, acrown, and a sole. The crown and/or the sole includes an FRP member thatis formed by a fiber reinforced plastic containing a fiber and a matrixresin. The FRP member has an average flexural modulus of greater than orequal to 25 GPa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a golf club head according to a firstembodiment;

FIG. 2 is an exploded perspective view of the head in FIG. 1;

FIG. 3 is a plan view of a head body of the head in FIG. 1;

FIG. 4 is a perspective view of the head body in FIG. 3;

FIG. 5A, FIG. 5B, FIG. 5C and FIG. 5D show examples of a laminatedconstitution of an FRP member;

FIG. 6 is a bottom view of a golf club head according to a secondembodiment;

FIG. 7 is, as with FIG. 1, the plan view of the golf club head accordingto the first embodiment, and shows cutoff lines for cutting out testpieces to be used for measuring flexural moduli in a 0-degree directionand a 90-degree direction of the FRP member;

FIG. 8A, FIG. 8B and FIG. 8C are diagrams illustrating the process ofmeasuring the flexural modulus of the FRP member;

FIG. 9A and FIG. 9B show laminated constitutions in Examples; and

FIG. 10 is a schematic diagram illustrating a toe-heel direction and aface-back direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments in detail with appropriatereference to the drawings.

FIG. 1 is a plan view of a head 100 according to a first embodiment asviewed from a crown side. FIG. 2 is an exploded perspective view of thehead 100. FIG. 3 is a plan view of a head body h1 as viewed from thecrown side. FIG. 4 is a perspective view of the head body h1.

The head 100 includes a striking face 102, a crown 104, a sole 106, anda hosel 108. The hosel 108 includes a hosel hole 108 a. The head 100 isa wood type golf club head. The inside of the head 100 is an emptyspace. That is, the head 100 is hollow. In the present embodiment, thehosel hole 108 a has a centerline that is a shaft axis line Z (describedlater).

As well shown in FIG. 2, the head 100 includes the head body h1 and anFRP member f1. The head body h1 includes the whole striking face 102.The head body h1 includes a part of the crown 104. The head body h1includes the whole sole 106. The head body h1 includes the whole hosel108.

The head body h1 forms portions except the FRP member f1. The head bodyh1 is made of a metal. The head body h1 may be formed by a single memberthat is integrally formed. Alternatively, the head body h1 may be formedby joining two or more members to each other.

The crown 104 includes an outer surface 104 a. The head body h1 includesa part of the crown outer surface 104 a. The FRP member f1 includes apart of the crown outer surface 104 a. The crown outer surface 104 a isconstituted by the head body h1 and the FRP member f1.

The head body h1 includes an opening 110. The opening 110 includes acontour 112. The contour 112 is an edge of the head body h1. The opening110 penetrates through the head 100 from the outside to the inside ofthe head 100. In other words, the opening 110 penetrates through thehead 100 from the outside to the hollow portion of the head 100.

The opening 110 is provided on the crown 104. The opening 110 can beprovided at a location that corresponds to the location of the FRPmember f1. For example, when the FRP member f1 is provided on the sole106, the opening 110 can also be provided on the sole 106. For example,when the FRP member f1 is provided so as to extend from the sole 106into the crown 104, the opening 110 can also be provided so as to extendfrom the sole 106 into the crown 104.

The head body h1 includes the crown outer surface 104 a which forms thesurface of the crown 104, a stepped portion 116, and a support portion118. The stepped portion 116 has a shape that corresponds to the shapeof the contour of the FRP member f1. The stepped portion 116 is formedto coincide with the peripheral edge of the FRP member f1. The steppedportion 116 has a height that corresponds to the thickness of theperipheral edge of the FRP member f1. The crown outer surface 104 a hasno step on a boundary k1 between the head body h1 and the FRP member f1.Note that the boundary k1 is not visually recognized in thefinished-product head 100 which has been subjected to surface treatmentsuch as painting.

The support portion 118 abuts against the inner surface of the FRPmember f1. The support portion 118 supports the FRP member f1 from theinside of the head 100. The head body h1 is joined to the FRP member f1on the support portion 118. The method of this joining is adhesion withan adhesive.

The FRP member f1 has a plate-like shape as a whole. The FRP member f1is curved so as to project toward the outside of the head 100. The outersurface of the FRP member f1 constitutes the crown outer surface 104 a.The FRP member f1 has a constant thickness. Alternatively, the FRPmember f1 may have an inconstant thickness.

Of the FRP member f1, a portion located inside the contour 112 of theopening 110 is not supported by the support portion 118 of the head bodyh1. Of the crown 104, the portion located inside the contour 112 of theopening 110 is formed by only the FRP member f1. This portion formed byonly the FRP member f1 is also referred to as an FRP alone portion. TheFRP member f1 includes an FRP alone portion f11. A central portion ofthe FRP member f1 is the FRP alone portion f11. The outer surface of theFRP alone portion f11 constitutes the crown outer surface 104 a. Theinner surface of the FRP alone portion f11 faces the hollow portion ofthe head 100. The peripheral edge of the FRP member f1 is glued to thesupport portion 118. Preferably, two test pieces for measuring anaverage flexural modulus (detailed later) are cut out from the FRP aloneportion f11.

The FRP member f1 is formed by only a fiber reinforced resin. The FRPmember f1 has a specific gravity different from the specific gravity ofthe head body h1. The specific gravity of the FRP member f1 is smallerthan the specific gravity of the head body h1. The FRP member f1enhances the degree of freedom in location of the center of gravity ofthe head 100. The FRP member f1 contributes to lowering of the center ofgravity of the head 100. The FRP member f1 enhances the degree offreedom in weight distribution of the head 100. The FRP member f1contributes to increase of the moment of inertia of the head 100. Aresin in the present application means a concept including resincompositions.

The structure and manufacturing method of the FRP member f1 are notlimited. The FRP member f1 is preferably formed by one or more prepregs.In the present embodiment, the FRP member f1 is formed by laminatedprepregs. The prepregs are not limited. Examples of the prepregs includea UD prepreg and a prepreg in which fibers are woven. The prepreg inwhich fibers are woven is also referred to as a woven prepreg. In the UDprepreg, fibers are oriented in one direction. The term UD stands forunidirectional. The UD prepreg is used in the present embodiment. TheFRP member f1 may include a layer formed by a prepreg that is not the UDprepreg. For example, the FRP member f1 may include a woven layer. Thewoven layer means a layer formed by the woven prepreg.

The FRP member f1 in the present embodiment is formed by a plurality ofUD prepregs laminated on each other. Cut prepregs are laminated in theFRP member f1. The FRP member f1 includes a plurality of layers. Oneprepreg forms one layer.

The FRP member f1 in the present embodiment includes two layers,respective fibers of which are oriented at different angles from eachother. The FRP member f1 includes a layer having a fiber-orientationangle θ of a first angle θ1, and a layer having a fiber-orientationangle θ of a second angle θ2. The FRP member f1 includes the two layershaving different fiber-orientation angles, which enables to reduceanisotropy of the FRP member f1. By enhancing rigidities in differentbending directions, sound at impact can be improved.

FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D show examples of the laminatedconstitution of the FRP member f1. FIG. 9A and FIG. 9B described latershow laminated constitutions in examples. These diagrams schematicallyshow prepregs constituting the FRP member f1 with D shapes. Theseprepregs are actually cut out into a shape that corresponds to thecontour shape of the FRP member f1. One prepreg forms one layer. Theseprepregs are laminated and subjected to thermoforming process using amold to obtain the FRP member f1 constituted by the plurality of layers.

In the embodiment of FIG. 5A, the number N of the layers of the FRPmember f1 is four. These four layers are termed a first layer s1, asecond layer s2, a third layer s3, and a fourth layer s4 in order frominside. The first layer s1 is the innermost layer. The fourth layer s4is the outermost layer. In the embodiment of FIG. 5B, the number N ofthe layers of the FRP member f1 is five. These five layers are termed afirst layer s1, a second layer s2, a third layer s3, a fourth layer s4,and a fifth layer s5 in order from inside. The first layer s1 is theinnermost layer. The fifth layer s5 is the outermost layer. In theembodiment of FIG. 5C, the number N of the layers of the FRP member f1is six. These six layers are termed a first layer s1, a second layer s2,a third layer s3, a fourth layer s4, a fifth layer s5, and a sixth layers6 in order from inside. The first layer s1 is the innermost layer. Thesixth layer s6 is the outermost layer. In the embodiment of FIG. 5D, thenumber N of the layers of the FRP member f1 is eight. These eight layersare termed a first layer s1, a second layer s2, a third layer s3, afourth layer s4, a fifth layer s5, a sixth layer s6, a seventh layer s7,and an eighth layer s8 in order from inside. The first layer s1 is theinnermost layer. The eighth layer s8 is the outermost layer. In theseembodiments, all the layers are UD layers formed by UD prepregs.

The number of the layers of the FRP member f1 is not limited. From thestandpoint of strength and reduction of the anisotropy, the number ofthe layers of the FRP member f1 is preferably greater than or equal to2, more preferably greater than or equal to 3, and still more preferablygreater than or equal to 4. From the standpoint of weight reduction andproductivity, the number of the layers of the FRP member f1 ispreferably less than or equal to 10, more preferably less than or equalto 9, and still more preferably less than or equal to 8.

The laminated constitution of the FRP member f1 may have a laminationsymmetric property. The lamination symmetric property in the presentapplication means that an n-th outer layer counting from a neutralsurface and an n-th inner layer counting from the neutral surface have asubstantially same specification. The “n” is an integer of greater thanor equal to 1. The FRP member f1 is formed by laminating the prepregs sothat the laminated layers are symmetrical with respect to the neutralsurface, thus inhibiting coupling effects such as distortion which mightbe caused by bending. In addition, the symmetrically laminated layerswith respect to the neutral surface facilitate keeping the location ofthe neutral surface at the center in the thickness direction of the FRPmember f1. Therefore, improvement in rigidity (flexural rigidity) of theFRP member f1 is facilitated. The lamination symmetric property cancontribute to enhancing the rigidity of the FRP member f1 whilecontrolling its thickness. The FRP member f1 having a high rigidity cancontribute to improvement in sound at impact.

The number of the UD-prepreg layers in the FRP member f1 is denoted byN. When N is an even number, the neutral surface means a boundarybetween a [N/2]-th layer counting from inside and a [(N/2)+1]-th layercounting from inside. When N is an odd number, the neutral surface means[(N/2)+1]-th layer itself counting from inside.

The lamination symmetric property can be defined per specification.Examples of the specifications include a fiber-orientation angle, alayer thickness, the kind of carbon fibers, fiber content, and the kindof prepregs.

Hereinafter, the neutral surface and the lamination symmetric propertyare specifically explained.

As shown in FIG. 5A, when the number N of the layers of the FRP memberf1 is 4, for example, the neutral surface NP is the boundary between thesecond layer s2 and the third layer s3.

When the embodiment of FIG. 5A satisfies the following (a1) and (a2),this embodiment is defined as having a lamination symmetric property infiber-orientation angles.

(a1) The fiber-orientation angle of the first layer s1 is substantiallyequal to the fiber-orientation angle of the fourth layer s4.

(a2) The fiber-orientation angle of the second layer s2 is substantiallyequal to the fiber-orientation angle of the third layer s3.

The lamination symmetric property in fiber-orientation angles cancontribute to improvement in sound at impact.

Note that the term “substantially” used for the fiber-orientation anglemeans that a margin of error of ±10 degrees (preferably ±5 degrees) isacceptable. Normally, the outer surface of the head 100 is formed with afree-form curved surface, not a flat surface. For this reason, a certaindegree of margin of error in the fiber-orientation angle is inevitable.

Similarly, lamination symmetric properties in other specifications arealso defined. For example, when the number N of the layers is 4, the FRPmember f1 satisfying the following (a3) and (a4) has a laminationsymmetric property in layer thicknesses.

(a3) The layer thickness of the first layer s1 is substantially equal tothe layer thickness of the fourth layer s4.

(a4) The layer thickness of the second layer s2 is substantially equalto the layer thickness of the third layer s3.

The lamination symmetric property in layer thicknesses can contribute toimprovement in sound at impact.

Note that the term “substantially” used for the layer thickness meansthat a margin of error of ±10% (preferably ±5%) is acceptable. Normally,some matrix resin fluidizes during the process of forming the FRP memberf1. For this reason, a certain degree of margin of error in the layerthickness is inevitable.

Similarly, when the number N of the layers is 4, the FRP member f1satisfying the following (a5) and (a6) has a lamination symmetricproperty in kinds of prepregs.

(a5) The kind of prepreg of the first layer s1 is equal to the kind ofprepreg of the fourth layer s4.

(a6) The kind of prepreg of the second layer s2 is equal to the kind ofprepreg of the third layer s3.

The lamination symmetric property in kinds of prepregs can contribute toimprovement in sound at impact.

The kind of prepreg can be determined by a product number of theprepreg.

As shown in FIG. 5B, when the number N of the layers of the FRP memberf1 is 5, for example, the neutral surface NP is the third layer s3itself.

When the embodiment of FIG. 5B satisfies the following (b1) and (b2),this embodiment has a lamination symmetric property in fiber-orientationangles.

(b1) The fiber-orientation angle of the first layer s1 is substantiallyequal to the fiber-orientation angle of the fifth layer s5.

(b2) The fiber-orientation angle of the second layer s2 is substantiallyequal to the fiber-orientation angle of the fourth layer s4.

When the number N of the layers is 5, the FRP member f1 satisfying thefollowing (b3) and (b4) has a lamination symmetric property in layerthicknesses.

(b3) The layer thickness of the first layer s1 is substantially equal tothe layer thickness of the fifth layer s5.

(b4) The layer thickness of the second layer s2 is substantially equalto the layer thickness of the fourth layer s4.

When the number N of the layers is 5, the FRP member f1 satisfying thefollowing (b5) and (b6) has a lamination symmetric property in kinds ofprepregs.

(b5) The kind of prepreg of the first layer s1 is equal to the kind ofprepreg of the fifth layer s5.

(b6) The kind of the prepreg of the second layer s2 is equal to the kindof the prepreg of the fourth layer s4.

When N is an even number as shown in FIG. 5C and FIG. 5D, the neutralsurface NP and the lamination symmetric properties are defined in thesimilar manner as in the embodiment of FIG. 5A. In the embodiment ofFIG. 5C (N=6), the neutral surface NP is a boundary between the thirdlayer s3 and the fourth layer s4. In the embodiment of FIG. 5D (N=8),the neutral surface NP is a boundary between the fourth layer s4 and thefifth layer s5.

The term “fiber-orientation angle θ” is defined in present application.The fiber-orientation angle θ is determined by using a face-backdirection as 0 degree. The angle θ is determined on the planar view ofthe head. The face-back direction is defined as follows. With referenceto FIG. 10, a head is placed at a predetermined lie angle and real loftangle on a horizontal plane HP, which is referred to as a referencestate, and a perpendicular plane VP that is perpendicular to thehorizontal plane HP and includes a shaft axis line Z of the head isdetermined. The direction of an intersection line NL between theperpendicular plane VP and the horizontal plane HP is defined as atoe-heel direction. A direction that is perpendicular to the toe-heeldirection and parallel to the horizontal plane HP is defined as theface-back direction. The predetermined lie angle and real loft angle areshown in a product catalog, for example.

From the standpoint of reducing anisotropy and enhancing rigidity andstrength in a plurality of directions, the FRP member f1 may include twokinds of angles θ. That is, the FRP member f1 may include a layer havinga fiber-orientation angle θ of a first angle θ1, and a layer having afiber-orientation angle θ of a second angle θ2. Moreover, the FRP memberf1 may include three kinds of angles θ. That is, the FRP member f1 mayinclude a layer having a fiber-orientation angle θ of a first angle θ1,a layer having a fiber-orientation angle θ of a second angle θ2, and alayer having a fiber-orientation angle θ of a third angle θ3. Moreover,the FRP member f1 may include four or more kinds of angles θ. Examplesof the angle θ include 0 degree, ±30 degrees, ±45 degrees, ±60 degrees,±75 degrees, and 90 degrees. A margin of error of ±10 degrees(preferably ±5 degrees) is acceptable in the fiber-orientation angle θ.

In a preferable example, the FRP member f1 includes a layer having afiber-orientation angle θ of 0 degree (0-degree layer). An impact forceapplied to the head from a ball at impact acts in the face-backdirection. The 0-degree layer is effective in enhancing the rigidity andstrength of the FRP member f1 against the impact force. The 0-degreelayer can contribute to improvement in sound at impact.

In another preferable example, the FRP member f1 includes a layer(0-degree layer) having a fiber-orientation angle θ of 0 degree, and alayer (90-degree layer) having a fiber-orientation angle θ of 90degrees. As described above, the 0-degree layer can effectively enhancethe rigidity of the FRP member f1 against the impact force. The90-degree layer can enhance the rigidity of the FRP member f1 in adirection which is difficult to reinforce with the 0-degree layer.

In still another preferable example, the FRP member f1 includes the0-degree layer and the 90-degree layer, and has the lamination symmetricproperty in fiber-orientation angles. For example, in the embodiment ofFIG. 5A, the first layer s1 and the fourth layer s4 may be the 0-degreelayers, and the second layer s2 and the third layer s3 may be the90-degree layers. For example, in the embodiment of FIG. 5B, the firstlayer s1 and the fifth layer s5 may be the 0-degree layers, the secondlayer s2 and the fourth layer s4 may be 90-degree layers. For example,in the embodiment of FIG. 5C, the first layer s1, the third layer s3,the fourth layer s4 and the sixth layer s6 may be the 0-degree layers,and the second layer s2 and the fifth layer s5 may be the 90-degreelayers. For example, in the embodiment of FIG. 5D, the first layer s1,the third layer s3, the sixth layer s6, and the eighth layer s8 may bethe 0-degree layers, and the second layer s2, the fourth layer s4, thefifth layer s5, and the seventh layer s7 may the 90-degree layers. Inthese examples, respective outermost layers are the 0-degree layers.

The embodiment of FIG. 5B has the lamination symmetric property infiber-orientation angles regardless of the fiber-orientation angle θ ofthe third layer s3. In the embodiment of FIG. 5B, the number N of thelayers is an odd number, and thus the neutral surface is the third layers3 itself. When the number N of the layers is an odd number,specifications of a layer that forms the neutral surface NP do notinfluence the lamination symmetric property.

As described above, the FRP member f1 may be provided on the sole. Ahead 200 according to a second embodiment shown in FIG. 6 includes theFRP member f1 provided on the sole.

FIG. 6 is a bottom view of the head 200 according to the secondembodiment as viewed from the sole side. The head 200 includes astriking face 202, a crown (not shown in the drawing), a sole 206, and ahosel 208. The head 200 includes a head body h1 and the FRP member f1.The head body h1 includes the whole striking face 202. The head body h1includes the whole crown. The head body h1 includes a part of the sole206. The head body h1 includes the whole hosel 208.

The head body h1 forms portions except the FRP member f1. The head bodyh1 is made of a metal. The head body h1 includes an opening 210 and asupport portion 218. The opening 210 includes a contour 212. The contour212 is an edge of the head body h1. The opening 210 penetrates throughthe head 200 from the outside to the inside of the head 200. The opening210 is provided on the sole 206. The opening 210 is provided at alocation that corresponds to the location of the FRP member f1. Thesupport portion 218 is located on the circumference of the opening 210.The support portion 218 supports the FRP member f1 from the inside ofthe head 200. The support portion 218 abuts against the inner surface ofthe FRP member f1. The head body h1 is joined to the FRP member f1 onthe support portion 218. The method of this joining is adhesion with anadhesive. The FRP member f1 covers the opening 210. The outer surface ofthe sole 206 has no step on a boundary k1 between the head body h1 andthe FRP member f1.

One example of the manufacturing method for the FRP member f1 includesthe following steps:

(1) stacking prepregs according to a designed laminated constitution andpressing the stacked prepregs onto each other to obtain laminatedsheets;

(2) cutting the laminated sheets into a predetermined-shape to obtain apiece to be molded; and

(3) heating and pressurizing the piece to be molded by using a mold toobtain the FRP member.

From the standpoint of sound at impact, the FRP member f1 has a resincontent of preferably less than or equal to 42% by weight, morepreferably less than or equal to 40% by weight, still more preferablyless than or equal to 35% by weight, and yet still more preferably lessthan or equal to 30% by weight. From the standpoint of formability, theresin content of the FRP member f1 is preferably greater than or equalto 15% by weight, and more preferably greater than or equal to 20% byweight. When multiple kinds of prepregs are used, the resin content canbe calculated by weighted average of respective resin contents of theprepregs. That is, the resin content means the resin content of thewhole FRP member f1.

From the standpoint of sound at impact, the matrix resin has a glasstransition temperature Tg of preferably higher than or equal to 120° C.,more preferably higher than or equal to 150° C., still more preferablyhigher than or equal to 180° C., and yet still more preferably higherthan or equal to 200° C. An excessively high glass transitiontemperature Tg of the matrix resin requires a facility having a highheating capability, or takes longer time for molding, thereby reducingproductivity. In addition, a matrix resin having such a high Tg might bedifficult to obtain. In these respects, the glass transition temperatureTg of the matrix resin is preferably lower than or equal to 300° C., andmore preferably lower than or equal to 280° C. When multiple kinds ofprepregs are used, glass transition temperatures Tg of all the prepregspreferably satisfy the above values.

The glass transition temperature of a matrix resin can be measured asfollows. In this measurement, a test piece made of a matrix resin to bemeasured is prepared. This test piece has a length of 55 mm, a width of12.7 mm, and a thickness of 2 mm. According to ASTM D-7028, a dynamicviscoelasticity measurement device is used to measure a storage modulusE′ in flexure mode under conditions of a frequency of 1 Hz and a heatingrate of 5° C./min. In a graph made by plotting values of log E′ againsttemperature, a temperature at an intersection point between a tangentline of a flat region before the transition of log E′ and a tangent lineat an inflection point of a transition region of log E′ can bedetermined as the glass transition temperature.

The fibers (reinforcing fibers) of the FRP member f1 may include ametallic fiber. The metallic fiber can contribute to improvement insound at impact. In this case, the reinforcing fibers preferably includea carbon fiber and a metallic fiber.

Examples of the metallic fiber include an aluminum fiber, a magnesiumfiber, a titanium fiber, a nickel fiber, a nickel-titanium alloy fiber(Ni—Ti wire), a copper fiber, a tungsten fiber, a molybdenum fiber, aberyllium fiber, stainless steel fiber, and a boron fiber. The names ofthese metallic fibers show materials of the fibers. The metallic fibermay contain a different material as a core material in addition to themetal. For example, the boron fiber may be formed by vapor deposition ofboron onto the surface of a tungsten wire that is used as the corematerial. Note that the aluminum fiber is a concept that includes analuminum alloy fiber. This holds true for other metallic fibers.

When the carbon fiber is used for the reinforcing fibers, from thestandpoint of obtaining a high-pitched sound at impact, the carbon fiberpreferably has a greater tensile elastic modulus. The tensile elasticmodulus of the carbon fiber is preferably greater than or equal to 240GPa, more preferably greater than or equal to 300 GPa, and still morepreferably greater than or equal to 330 GPa. From the standpoint ofstrength, a PAN-based carbon fiber is preferably used. The tensileelastic modulus of the carbon fiber is preferably less than or equal to900 GPa, and more preferably less than or equal to 800 GPa. The value ofthe tensile elastic modulus is obtained by measuring the carbon fiber inaccordance with JIS R 7601: 1986 “Testing methods for carbon fiber”.

The kind of the matrix resin is not limited. Examples of the matrixresin include a thermoplastic resin and a thermosetting resin. Examplesof the thermosetting resin include an unsaturated polyester resin, anepoxy resin, a vinyl ester resin, a bismaleimide resin, a phenol resin,a cyanate resin, and a polyimide resin. Examples of the thermoplasticresin include a nylon resin (PA), a polypropylene resin (PP), apolyphenylene sulfide resin (PPS), a polyetherimide resin (PEI), apolycarbonate resin (PC), a polyethylene terephthalate resin (PET), apolyether ketone resin (PEK), a polyether ether ketone resin (PEEK), anda polyether ketone ketone resin (PEKK). From the standpoint offormability and versatility, the epoxy resin is preferable.

From the standpoint of enhancing the degree of freedom in design of thehead, the FRP alone portion f11 preferably has a large area (area of theopening 110). When the FRP member f1 is provided on the crown, a ratioRf of the area of the FRP alone portion f11 to the area of the crown 104is preferably greater than or equal to 40%, and more preferably greaterthan or equal to 50%. From the standpoint of sound at impact, the ratioRf is preferably less than or equal to 90%, and more preferably lessthan or equal to 80%. The ratio Rf is determined in the plan view asviewed from the crown side.

From the standpoint of enhancing the degree of freedom in design of thehead, the FRP member f1 has a weight of preferably less than or equal to30 g, more preferably less than or equal to 25 g, and still morepreferably less than or equal to 20 g. From the standpoint of strengthof the FRP member f1, the weight of the FRP member f1 is preferablygreater than or equal to 5 g, and more preferably greater than or equalto 10 g.

From the standpoint of enhancing rigidity, the FRP member f1 has athickness of preferably greater than or equal to 0.4 mm, more preferablygreater than or equal to 0.5 mm, and still more preferably greater thanor equal to 0.6 mm. From the standpoint of reducing weight, thethickness of the FRP member f1 is preferably less than or equal to 1.5mm, more preferably less than or equal to 1.2 mm, and still morepreferably less than or equal to 1.0 mm. In view of lowering the centerof gravity of the head, when the FRP member f1 is provided on the crown,the thickness of the FRP member f1 is particularly preferably less thanor equal to 0.8 mm. In view of sound at impact and lowering the centerof gravity of the head, when the FRP member f1 is provided on the sole,the thickness of the FRP member f1 is preferably less than or equal to1.0 mm and preferably greater than or equal to 0.8 mm.

From the standpoint of reducing weight, the FRP member f1 has a specificgravity of preferably less than or equal to 2.0, more preferably lessthan or equal to 1.8, and still more preferably less than or equal to1.7. From the standpoint of increasing fiber content and enhancingrigidity, the specific gravity of the FRP member f1 is preferablygreater than or equal to 1.2, more preferably greater than or equal to1.3, and still more preferably greater than or equal to 1.4.

A large-sized head includes a hollow portion having a large volume and ahead outer shell having a small thickness. For this reason, such alarge-sized head has a big sound at impact. The technique of the presentdisclosure is effective in heads having a big sound at impact. The headhas a volume of preferably greater than or equal to 400 cc, morepreferably greater than or equal to 420 cc, and still more preferablygreater than or equal to 440 cc. From the standpoint of golf rules, thehead volume is preferably less than or equal to 470 cc, and morepreferably less than or equal to 460 cc. For large-sized heads such as adriver, the head weight is preferably set to greater than or equal to175 g and less than or equal to 225 g.

The FRP member f1 improves the degree of freedom in weight distributionof the head, which enables to enhance a moment of inertia of the head.The head has a left-and-right moment of inertia of preferably greaterthan or equal to 450×10⁻⁶ kg·m², and more preferably greater than orequal to 470×10⁻⁶ kg·m². In view of restriction on head volume, theleft-and-right moment of inertia of the head is preferably less than orequal to 590×10⁻⁶ kg·m².

In the head which is in the reference state, a vertical line that passesthrough the center of gravity of the head and is perpendicular to thehorizontal plane HP is determined. The left-and-right moment of inertiameans a moment of inertia about the vertical line. The left-and-rightmoment of inertia can be measured by using MOMENT OF INERTIA MEASURINGINSTRUMENT MODEL NO. 005-002 manufactured by INERTIA DYNAMICS.

The FRP member f1 improves the degree of freedom in weight distributionof the head, which enables to increase a depth of the center of gravityof the head. The depth of the center of gravity of the head ispreferably greater than or equal to 20 mm, and more preferably greaterthan or equal to 22 mm. In view of restriction on head volume, the depthof the center of gravity of the head is preferably less than or equal to40 mm, and more preferably less than or equal to 35 mm. The depth of thecenter of gravity of the head in the present application means theshortest distance between the shaft axis line Z and the center ofgravity of the head. This distance is measured along the face-backdirection.

[Average Flexural Modulus of FRP Member]

In the present application, the average flexural modulus of the FRPmember f1 means an average value of a flexural modulus in a 0-degreedirection and a flexural modulus in a 90-degree direction. From thestandpoint of sound at impact, the average flexural modulus ispreferably greater than or equal to 25 GPa.

The flexural modulus of the FRP member f1 is measured by using testpieces that are cut out from the FRP member f1. FIG. 7 is a plan view ofthe head 100 and shows lines along which the test pieces are cut out. Atwo-dot chain line shows a line along which a test piece 300 used formeasuring the flexural modulus in the 0-degree direction is cut out. Adashed line shows a line along which a test piece 302 used for measuringthe flexural modulus in the 90-degree direction is cut out. The testpiece 300 and the test piece 302 have the same dimensions. The averagevalue of the flexural modulus of the test piece 300 and the flexuralmodulus of the test piece 302 is the average flexural modulus of the FRPmember f1.

In the planar view (FIG. 7) of the head 100, the test piece 300 is arectangle having a long side of X mm and a short side of Y mm. The longside is parallel to the face-back direction. X is greater than Y. In theplanar view of the head 100, the test piece 302 is a rectangle having along side of X mm and a short side of Y mm. The long side is parallel tothe toe-heel direction. From the standpoint of stability of the FRPmember f1 during measurement, X is preferably greater than or equal to40 mm, more preferably greater than or equal to 50 mm, and still morepreferably greater than or equal to 55 mm. A smooth measurement can beperformed by adding a structure for preventing displacement of the testpiece to a measuring jig particularly when the length X is short. Theshort side length Y is set to 20 mm.

A reference sign Gf in FIG. 7 shows a center of figure of the FRP memberf1. The figure center Gf is the center of figure in the planar view(FIG. 7) of the head 100. A reference sign G1 in FIG. 7 shows a centerof figure of the test piece 300. The figure center G1 is the center offigure in the planar view (FIG. 7) of the head 100. A reference sign G2in FIG. 7 shows a center of figure of the test piece 302. The figurecenter G2 is the center of figure in the planar view (FIG. 7) of thehead 100. The test piece 300 is cut out such that the figure center G1of the test piece 300 coincides with the figure center Gf of the FRPmember f1. The test piece 302 is cut out such that the figure center G2of the test piece 302 coincides with the figure center Gf of the FRPmember f1. At least two heads are needed for preparing the test piece300 and the test piece 302.

The locations and dimensions of the lines along which the test piecesare cut out are determined in the plan view (planar view) of the head100, such as FIG. 7. When the FRP member is located on the sole, thelocations and dimensions of the lines along which the test pieces arecut out are determined in a bottom view (planar view), such as FIG. 6.When the FRP member extends from the crown into the sole, the locationsand dimensions of the lines along which the test pieces are cut out aredetermined in a figure having a larger area of the FRP member betweenthe plan view and the bottom view of the head.

FIG. 8A, FIG. 8B and FIG. 8C are sectional views showing the process ofmeasuring the flexural modulus of the FRP member f1. As shown in FIG.8A, the test piece 300 or the test piece 302 is placed on a measuringjig 310 for the measurement. The measuring jig 310 includes a firstsupporting edge E1, a second supporting edge E2, a first upper surface312, a second upper surface 314, and a gap 316. The first supportingedge E1 is horizontal, and the second supporting edge E2 is alsohorizontal. The first supporting edge E1 is parallel to the secondsupporting edge E2. The first supporting edge E1 and the secondsupporting edge E2 have the same height (same location in the verticaldirection). The gap 316 is located between the first upper surface 312and the second upper surface 314. The gap 316 is located between thefirst supporting edge E1 and the second supporting edge E2. The firstsupporting edge E1 is an edge of the first upper surface 312 and facesthe gap 316. The second supporting edge E2 is an edge of the secondupper surface 314 and faces the gap 316. The first upper surface 312 isinclined so as to go downward in the vertical direction as going awayfrom the gap 316. The second upper surface 314 is inclined so as to godownward in the vertical direction as going away from the gap 316. Thefirst supporting edge E1 and the second supporting edge E2 are vertexesof acute angles. As shown in FIG. 8A, the gap 316 has a width of 30 mm.This width is measured along a direction (hereinafter referred to as agap direction) of a straight line that is horizontal and perpendicularto the first supporting edge E1 and the second supporting edge E2. Eachof the test pieces 300 and 302 is placed so that its figure center G1 orG2 coincides with the center of the gap 316 in the gap direction.

Sectional shapes of the first supporting edge E1 and the secondsupporting edge E2 have a roundness. The roundness has a curvatureradius of 1.5 mm.

Each of the test pieces 300 and 302 is placed so that its long sides areparallel to the gap direction when viewed from above. Therefore, theshort sides of each test piece 300, 302 are parallel to the firstsupporting edge E1 and the second supporting edge E2 when viewed fromabove. Each test piece 300, 302 is aligned so that its figure center G1or G2 coincides with the center of the gap 316. As shown in FIG. 8A,before the test is started, each test piece 300, 302 can be a state inwhich the test piece is not brought into contact with the firstsupporting edge E1 or the second supporting edge E2.

Each test piece 300, 302 is pressed downward in the vertical directionby using an indenter 320. The location of the indenter 320 coincideswith the center of the gap 316 in the gap direction. The indenter 320has a convex-shaped tip end. In a cross section that is parallel to thegap direction, the shape of the tip end of the indenter 320 is a convexline having a curvature radius of 4 mm. In a cross section that isperpendicular to the gap direction, the shape of the tip end of theindenter 320 is a straight line. The straight line is a set of vertexesof the tip end of the indenter 320 and is parallel to the firstsupporting edge E1 and the second supporting edge E2. The tip end of theindenter 320 abuts against each test piece 300, 302.

The indenter 320 is moved downward in the vertical direction at a speedof 5 mm/min to obtain a stress-strain curve.

As the move of the indenter 320 progresses, a lower-surface referencepoint C1 of the test piece 300 or 302 is gradually lowered. Thelower-surface reference point C1 means a point that is present on thelower surface (inner surface) of the test piece and located at alowermost point on the back side of an indenter contacting region. Ofthe upper surface of the test piece, a region that is brought intocontact with the indenter 320 is referred to as the indenter contactingregion. Of the lower surface of the test piece, a region locateddownward in the vertical direction of the indenter contacting region isreferred to as the back side of the indenter contacting region.

The move of the indenter 320 moves the lower-surface reference point C1to as low as the height of the first supporting edge E1 and the secondsupporting edge E2. This position of the indenter 320 is defined as areference position. A stress when the indenter 320 is lowered by 0.1 mmfrom the reference point is denoted by of (MPa), a strain at thisposition is denoted by ε1, a stress when the strain is increased by 0.2%from the strain ε1 is denoted by σ2, a strain at this position isdenoted by ε2, and the flexural modulus (GPa) is calculated by thefollowing formula:

Flexural Modulus=(σ2−σ1)/((ε2−ε1)×1000).

The stress σ (MPa) is calculated by the following formula:

σ=3FL/2bh ².

In the above formula, F denotes a testing force (N), L denotes a span(mm) between supporting points, b denotes the width (mm) of the testpiece, and h denotes the thickness (mm) of the test piece. The span Lbetween the supporting points is 30 mm. The width b of the test piece isslightly greater than Y mm (20 mm), because the width b is measuredalong the curve of the test piece.

A strain ε is calculated by the following formula:

ε=6sh/L ².

In the above formula, s denotes an amount (mm) of deformation relativeto the reference position, L denotes the span (mm) between thesupporting points, and h denotes the thickness (mm) of the test piece.The span L between the supporting points is 30 mm. The amount s ofdeformation for calculating s1 is 0.1 mm.

[Modal Damping Ratio]

When a ball collides with a head, the head surface vibrates. Thevibration of the head surface allows air to vibrate, thereby causing asound at impact. The vibration of the head surface can be expressed bysuperposing a plurality of characteristic modes on each other. Eachcharacteristic mode has a natural frequency and a shape of vibration.The shape of vibration is also referred to as a characteristic modeshape. Elements for determining a surface vibration in onecharacteristic mode are a characteristic mode shape, an amplitude, anatural frequency, and a modal damping ratio. The characteristic modeshape and the natural frequency can be determined by an eigenvalueanalysis (modal analysis). The modal damping ratio is highly correlatedwith duration of sound at impact. The duration (period of time duringwhich a sound continues) of the sound at impact can be lengthened bydecreasing the modal damping ratio. A long duration of the sound atimpact is perceived as a long-lasting echo of the sound at impact, whichis recognized as a good sound at impact. A high-pitched and long-lastingsound at impact is preferable. The modal damping ratio can be found byexperimental modal analysis.

For calculation of the modal damping ratio, a frequency responsefunction is firstly measured. An impact hammer, an accelerometer, and anFFT analyzer are used for this measurement. Model 086E80 manufactured byPCB Piezotronics, Inc. is used as the impact hammer. Model 352B10manufactured by PCB Piezotronics, Inc. is used as the accelerometer.Model DS2100 manufactured by ONO SOKKI CO., LTD. is used as the FFTanalyzer. The impact hummer and the accelerometer are connected to theFFT analyzer. A yarn is fixed to a neck end surface of a head to hangthe head with the yarn. The accelerometer is attached to a face center.The face center is a center of figure of the striking face of the headin the planar view. The impact hammer is used to hit predeterminedpoints for applying vibration to obtain a frequency response function.The predetermined points are set on the surface of the head whichincludes the figure center Gf of the FRP member f1. More specifically,the predetermined points are arbitrary points, and for example, arelocated at: a point separated by 20 mm toward the toe side from the facecenter; a point separated by 20 mm toward the heel side from the facecenter; a point separated by 10 mm upward from the face center; a pointseparated by 10 mm downward from the face center; the center of thecrown; and the center of the sole. The FFT analyzer is used forcalculation of the frequency response function. Model DS0221manufactured by ONO SOKKI CO., LTD. is used as an appurtenant softwareof the FFT analyzer.

The modal damping ratio is next calculated. The modal damping ratio iscalculated based on the frequency response function. The modal dampingratio is calculated by using a method of identification of modalparameters. The method of identification of modal parameters is alsoreferred to as curve fitting since modal parameters are determined so asto fit the curved line of the frequency response function in the method.A MDOF method (Multiple Degrees Of Freedom method) is used as the methodof curve fitting. Of the MDOF method, an orthogonal polynomial is used.A modal analysis software is used for calculating the modal dampingratio. As the modal analysis software, tradename “ME' scopeVES”manufactured by Vibrant Technology, Inc. is used.

The modal damping ratio of each characteristic mode shape is identifiedin the modal analysis. Among characteristic mode shapes having a naturalfrequency of greater than or equal to 3000 Hz and less than or equal to5000 Hz, one characteristic mode shape that has the largest amplitude ofthe figure center Gf of the FRP member f1 is specified. The frequency ofthe specified characteristic mode shape is referred to as a specificmodal frequency. The range of 3000 to 5000 Hz is a frequency range inwhich a maximum peak of sound at impact of golf club heads is likely toappear. The modal damping ratio of the specific modal frequency is alsoreferred to as a specific modal damping ratio. The duration of sound atimpact can be lengthened by decreasing the specific modal damping ratio.

[Measurement of Sound at Impact]

A head to be measured is attached to a golf club. The golf club isattached to a swing robot. The swing robot hits a teed-up ball with thegolf club at a head speed of 38 m/s. The hitting point is the facecenter. As the golf ball, trade name “XXIO SUPER SOFT X” manufactured bySUMITOMO RUBBER INDUSTRIES, LTD. is used. A microphone is placed at alocation separated by 30 cm toward the toe side from the tee to record atime-history wave form of the sound at impact. The time-history waveform is subjected to Fourier transformation by using an FFT analyzer tocalculate a sound-at-impact primary frequency. Model DS-2100manufactured by ONO SOKKI CO., LTD. is used as the FFT analyzer.

The sound-at-impact primary frequency means a lowest frequency in peakfrequencies. In actual measurements, minute peaks tend to occur due tonoise and the like. In this case, from the standpoint of excluding suchpeaks caused by noise and the like, the sound-at-impact primaryfrequency is selected from peaks having a sound pressure of greater thanor equal to a predetermined threshold. The threshold is determined basedon a sound pressure of the highest peak. The threshold can be set to[sound pressure of the highest peak−20 dB]. In actual measurements,sounds produced from the ball are also recorded. The sounds producedfrom the ball are normally around 1500 Hz. In this respect, peaks in theranges of greater than or equal to 1000 Hz and less than or equal to2000 Hz are ignored. The sound-at-impact primary frequency is highlycorrelated to a sound pitch that humans feel.

EXAMPLES Example 1

A face part of a head body was formed by forging. Of the head body,apart excluding the face part was formed by lost-wax precision casting.The forged part and the casted part were welded to each other to obtaina head body having the same structure as the head body h1 of the head100. The head body was made of a titanium alloy.

An FRP member was produced separately from the head body. Laminatedprepregs were placed in a mold and then pressed and heated to obtain theFRP member. The thickness of the FRP member was 0.75 mm. The laminatedconstitution of Example 1 is shown in FIG. 9A. The laminatedconstitution had eight layers of a first layer s1 to an eighth layer s8in order from inside. The first layer s1 was a 0-degree layer. Thesecond layer s2 was a 90-degree layer. The third layer s3 was a 0-degreelayer. The fourth layer s4 was a 90-degree layer. The fifth layer s5 wasa 90-degree layer. The sixth layer s6 was a 0-degree layer. The seventhlayer s7 was a 90-degree layer. The eighth layer s8 was a 0-degreelayer. All the layers were formed by the same UD prepreg. The FRP memberhad a lamination symmetric property in fiber-orientation angles. The FRPmember had a lamination symmetric property in layer thicknesses. The FRPmember had a lamination symmetric property in kinds of carbon fibers.The FRP member had a lamination symmetric property in fiber contents.The FRP member had a lamination symmetric property in kinds of prepregs.

As the UD prepreg, an epoxy prepreg having a high Tg manufactured byToray Industries, Inc. was used. This prepreg contained a carbon fiberas a reinforcing fiber. The matrix resin of the prepreg was an epoxyresin. The matrix resin had a glass transition temperature of 200° C.The carbon fiber had a tensile elastic modulus of 240 GPa. The prepreghad a resin content of 42% by weight.

The obtained FRP member was glued to an opening of a crown of the headbody by using an adhesive to obtain a head having the same structure asthe head 100. The head had a volume of 460 cc, a left-and-right momentof inertia of 470×10⁻⁶ kg·m², and a weight of 196 g. The head had adepth of the center of gravity of 28 mm. The obtained head was attachedto a tip end portion of a shaft, and a grip was attached to a butt endportion of the shaft, to obtain a golf club. Specifications andevaluation results of Example 1 are shown in below Table 1.

Example 2

Laminated prepregs were placed in a mold and then pressed and heated toform an FRP member. The thickness of the FRP member was 0.75 mm. Thelaminated constitution of the FRP member of Example 2 is shown in FIG.9B. The laminated constitution had six layers of a first layer s1 to asixth layer s6 in order from inside. The first layer s1 was a 0-degreelayer. The second layer s2 was a 90-degree layer. The third layer s3 wasa 0-degree layer. The fourth layer s4 was a 0-degree layer. The fifthlayer s5 was a 90-degree layer. The sixth layer s6 was a 0-degree layer.All the layers were formed by the same UD prepreg. The FRP member had alamination symmetric property in fiber-orientation angles. The FRPmember had a lamination symmetric property in layer thicknesses. The FRPmember had a lamination symmetric property in kinds of carbon fibers.The FRP member had a lamination symmetric property in fiber contents.The FRP member had a lamination symmetric property in kinds of prepregs.

A prepreg manufactured by Mitsubishi Chemical Corporation was used asthe UD prepreg. This prepreg contained a carbon fiber as a reinforcingfiber. The matrix resin of the prepreg was an epoxy resin. The matrixresin had a glass transition temperature of 120° C. The carbon fiber hada tensile elastic modulus of 400 GPa. The prepreg had a resin content of42% by weight.

The obtained FRP member was glued to the same head body as in Example 1by using an adhesive to obtain a head. The head was combined with thesame shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Example 2 are shown in belowTable 1.

Example 3

Laminated prepregs were placed in a mold and then pressed and heated toform an FRP member. The thickness of the FRP member was 0.75 mm. Thelaminated constitution of the FRP member of Example 3 is shown in FIG.9B. The laminated constitution had six layers of a first layer s1 to asixth layer s6 in order from inside. The first layer s1 was a 0-degreelayer. The second layer s2 was a 90-degree layer. The third layer s3 wasa 0-degree layer. The fourth layer s4 was a 0-degree layer. The fifthlayer s5 was a 90-degree layer. The sixth layer s6 was a 0-degree layer.All the layers were formed by the same UD prepreg.

A prepreg manufactured by Mitsubishi Chemical Corporation was used asthe UD prepreg. This prepreg contained a metallic fiber in addition to acarbon fiber as reinforcing fibers. The metallic fiber was anickel-titanium alloy fiber. The matrix resin of the prepreg was anepoxy resin. The matrix resin had a glass transition temperature of 120°C. The carbon fiber had a tensile elastic modulus of 240 GPa. Theprepreg had a resin content of 42% by weight.

The obtained FRP member was glued to the same head body as in Example 1by using an adhesive to obtain a head. The head was combined with thesame shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Example 3 are shown in belowTable 1.

Example 4

Laminated prepregs were placed in a mold and then pressed and heated toform an FRP member. The thickness of the FRP member was 0.75 mm. Thelaminated constitution of the FRP member of Example 4 is shown in FIG.9B. The laminated constitution had six layers of a first layer s1 to asixth layer s6 in order from inside. The first layer s1 was a 0-degreelayer. The second layer s2 was a 90-degree layer. The third layer s3 wasa 0-degree layer. The fourth layer s4 was a 0-degree layer. The fifthlayer s5 was a 90-degree layer. The sixth layer s6 was a 0-degree layer.All the layers were formed by the same UD prepreg.

A prepreg manufactured by Mitsubishi Chemical Corporation was used asthe UD prepreg. This prepreg contained a carbon fiber as a reinforcingfiber. The matrix resin of the prepreg was an epoxy resin. The matrixresin had a glass transition temperature of 120° C. The carbon fiber hada tensile elastic modulus of 240 GPa. The prepreg had a resin content of23% by weight.

The obtained FRP member was glued to the same head body as in Example 1by using an adhesive to obtain a head. The head was combined with thesame shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Example 4 are shown in belowTable 1.

Example 5

Laminated prepregs were placed in a mold and then pressed and heated toform an FRP member. The thickness of the FRP member was 0.75 mm. Thelaminated constitution of the FRP member of Example 5 is shown in FIG.9B. The laminated constitution had six layers of a first layer s1 to asixth layer s6 in order from inside. The first layer s1 was a 0-degreelayer. The second layer s2 was a 90-degree layer. The third layer s3 wasa 0-degree layer. The fourth layer s4 was a 0-degree layer. The fifthlayer s5 was a 90-degree layer. The sixth layer s6 was a 0-degree layer.All the layers were formed by the same UD prepreg.

A prepreg manufactured by Mitsubishi Chemical Corporation was used asthe UD prepreg. This prepreg contained a metallic fiber in addition to acarbon fiber as reinforcing fibers. The metallic fiber was anickel-titanium alloy fiber. The matrix resin of the prepreg was anepoxy resin. The matrix resin had a glass transition temperature of 120°C. The carbon fiber had a tensile elastic modulus of 240 GPa. Theprepreg had a resin content of 30% by weight.

The obtained FRP member was glued to the same head body as in Example 1by using an adhesive to obtain a head. The head was combined with thesame shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Example 5 are shown in belowTable 1.

Comparative Example 1

Laminated prepregs were placed in a mold and then pressed and heated toform an FRP member. The thickness of the FRP member was 0.75 mm. Thelaminated constitution had five layers of a first layer s1 to a fifthlayer s5 in order from inside. The first layer s1 was a 0-degree layer.The second layer s2 was a 90-degree layer. The third layer s3 was a0-degree layer. The fourth layer s4 was a 90-degree layer. The fifthlayer s5 was a 0-degree layer. All the layers were formed by the same UDprepreg.

A prepreg manufactured by Mitsubishi Chemical Corporation was used asthe UD prepreg. This prepreg contained a carbon fiber as a reinforcingfiber. The matrix resin of the prepreg was an epoxy resin. The carbonfiber had a tensile elastic modulus of 240 GPa. The prepreg had a resincontent of 42% by weight.

The obtained FRP member was glued to the same head body as in Example 1by using an adhesive to obtain a head. The head was combined with thesame shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Comparative Example 1 are shownin below Table 1.

Comparative Example 2

Casting was performed to obtain a resin molded member made of an epoxyresin. The resin molded member had a thickness of 0.75 mm. The resinmolded member had the same shape as the shape of the FRP members inExamples 1 to 6 and Comparative Example 1.

The obtained resin molded member was glued to the same head body as inExample 1 by using an adhesive to obtain a head. The head was combinedwith the same shaft and grip as in Example 1 to obtain a golf club.Specifications and evaluation results of Comparative Example 2 are shownin below Table 1.

TABLE 1 Specifications and Evaluation Results of Examples andComparative Examples Comp. Ex. 1 Comp. Ex. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Carbon Fiber contained not contained contained contained containedcontained contained Tensile Elastic 240 none 240 400 240 240 240 Modulusof Carbon Fiber (GPa) Metallic Fiber none none none none NiTi none NiTiKind of Matrix Resin epoxy epoxy epoxy epoxy epoxy epoxy epoxy GlassTransition 120 120 200 120 120 120 120 Temperature (° C.) Resin Content42 100 42 42 42 23 30 (% by weight) Average Flexural 23 8 55 64 33 55 57Modulus (GPa) Specific Gravity of 1.52 1.1 1.56 1.56 1.62 1.6 1.56 FRPmember Weight (g) of 18.2 13.2 18.7 18.7 19.4 19.2 18.7 FRP memberSpecific Modal 3380 2840 4230 4540 4450 4380 4450 Frequency (Hz)Specific Modal Damping 0.9 2.4 0.32 1.5 0.26 0.4 0.22 Ratio (%)Sound-at-Impact 3330 2840 4150 4480 3820 4360 4250 Primary Frequency(Hz) Sensuous Evaluation of — N Y Y Y Y Y Sound Pitch (against Comp. Ex.1)

Measurement methods for the evaluations were as described above.Sensuous evaluations were performed such that a person standing at alocation separated by 100 cm toward the toe side from the tee listenedsound at impact produced by the swing robot as described in the above“[Measurement of Sound at impact]”. The person determined whether thepitch of the sound at impact was higher or not as compared with that ofComparative Example 1 in the sensuous evaluations. Table 1 shows resultsof the sensuous evaluations by using “Y” or “N”, “Y” meaning that thesound at impact sounded higher-pitched than that of Comparative Example1, and “N” meaning that the sound at impact did not sound higher-pitchedthan that of Comparative Example 1.

Note that, in Comparative Example 2, since a characteristic mode shapehaving a natural frequency of 3000 to 5000 Hz did not exist, a naturalfrequency that is nearest to 3000 to 5000 Hz is shown as its specificmodal frequency in Table 1.

The FRP member of Example 1 contained the matrix resin which had a highglass transition temperature. For this reason, Example 1 had a highspecific modal frequency and a high sound-at-impact primary frequency.The FRP member of Example 2 contained the carbon fiber which had a hightensile elastic modulus. For this reason, Example 2 had a particularlygreat average flexural modulus of the FRP member, a high specific modalfrequency and a high sound-at-impact primary frequency. The FRP memberof Example 3 had a comparatively greater average flexural modulus. Thus,Example 3 had a comparatively high specific modal frequency and acomparatively high sound-at-impact primary frequency. The FRP member ofExample 3 contained the metallic fiber (Ni—Ti wire). Thus, Example 3 hada low specific modal damping ratio. The FRP member of Example 4 had alow resin content. For this reason, Example 4 had a high specific modalfrequency and a high sound-at-impact primary frequency. The FRP memberof Example 5 contained the metallic fiber and had a low resin content.For this reason, Example 5 had a high specific modal frequency and ahigh sound-at-impact primary frequency. The FRP member of Example 5contained the metallic fiber (Ni—Ti wire). Thus, Example 5 had a lowspecific modal damping ratio.

As shown in Table 1, Examples are higher evaluated as compared withComparative Examples.

The following clauses are disclosed regarding the above-describedembodiments.

[Clause 1]

A golf club head comprising:

a striking face;

a crown; and

a sole, wherein

the crown and/or the sole includes an FRP member formed by a fiberreinforced plastic that contains a fiber and a matrix resin, and

the FRP member has an average flexural modulus of greater than or equalto 25 GPa.

[Clause 2]

The golf club head according to clause 1, wherein

the fiber contains a carbon fiber, and

the carbon fiber has a tensile elastic modulus of greater than or equalto 300 GPa.

[Clause 3]

The golf club head according to clause 1 or 2, wherein

the fiber contains a metallic fiber.

[Clause 4]

The golf club head according to any one of clauses 1 to 3, wherein

the FRP member has a resin content of less than or equal to 40% byweight.

[Clause 5]

The golf club head according to any one of clauses 1 to 4, wherein

the matrix resin has a glass transition temperature of higher than orequal to 150° C.

[Clause 6]

The golf club head according to any one of clauses 1 to 5, wherein

the head has a weight of greater than or equal to 175 g and less than orequal to 225 g,

the head has a volume of greater than or equal to 400 cc, and

the head has a left-and-right moment of inertia of greater than or equalto 450×10⁻⁶ kg·m².

[Clause 7]

The golf club head according to any one of clauses 1 to 6, wherein

the FRP member has a weight of less than or equal to 20 g.

[Clause 8]

The golf club head according to any one of clauses 1 to 7, wherein

the FRP member is provided on the crown, and

the FRP member has a thickness of less than or equal to 0.8 mm.

[Clause 9]

The golf club head according to any one of clauses 1 to 8, wherein

the FRP member is provided on the crown, and

the head has a depth of a center of gravity of greater than or equal to20 mm.

[Clause 10]

The golf club head according to any one of clauses 1 to 7, wherein

the FRP member is provided on the sole, and

the FRP member has a thickness of less than or equal to 1.0 mm.

The above description is merely illustrative and various modificationscan be made without departing from the principles of the presentdisclosure.

What is claimed is:
 1. A golf club head comprising: a striking face; acrown; and a sole, wherein the crown and/or the sole includes an FRPmember formed by a fiber reinforced plastic that contains a fiber and amatrix resin, and the FRP member has an average flexural modulus ofgreater than or equal to 25 GPa.
 2. The golf club head according toclaim 1, wherein the fiber contains a carbon fiber, and the carbon fiberhas a tensile elastic modulus of greater than or equal to 300 GPa. 3.The golf club head according to claim 1, wherein the fiber contains ametallic fiber.
 4. The golf club head according to claim 1, wherein theFRP member has a resin content of less than or equal to 40% by weight.5. The golf club head according to claim 1, wherein the matrix resin hasa glass transition temperature of higher than or equal to 150° C.
 6. Thegolf club head according to claim 1, wherein the golf club head has aweight of greater than or equal to 175 g and less than or equal to 225g, the golf club head has a volume of greater than or equal to 400 cc,and the golf club head has a left-and-right moment of inertia of greaterthan or equal to 450×10⁻⁶ kg·m².
 7. The golf club head according toclaim 1, wherein the FRP member has a weight of less than or equal to 20g.
 8. The golf club head according to claim 1, wherein the FRP member isprovided on the crown, and the FRP member has a thickness of less thanor equal to 0.8 mm.
 9. The golf club head according to claim 1, whereinthe FRP member is provided on the crown, and the golf club head has adepth of a center of gravity of greater than or equal to 20 mm.
 10. Thegolf club head according to claim 1, wherein the FRP member is providedon the sole, and the FRP member has a thickness of less than or equal to1.0 mm.
 11. The golf club head according to claim 1, wherein the averageflexural modulus is an average value of a flexural modulus in a 0-degreedirection and a flexural modulus in a 90-degree direction, the 0-degreedirection being a face-back direction, and the 90-degree direction beinga toe-heel direction.
 12. The golf club head according to claim 1,wherein the golf club head further comprises a head body that includesan opening and is made of a metal, the opening is disposed in the crownor the sole, or extends from the sole into the crown, and the FRP membercovers the opening.
 13. The golf club head according to claim 12,wherein the fiber contains a carbon fiber and a metallic fiber.
 14. Thegolf club head according to claim 13, wherein the matrix resin has aglass transition temperature of higher than or equal to 150° C.
 15. Thegolf club head according to claim 14, wherein the carbon fiber has atensile elastic modulus of greater than or equal to 300 GPa.
 16. Thegolf club head according to claim 15, wherein the FRP member has a resincontent of less than or equal to 40% by weight.